In a flock of White Leghorn chickens, composed of hens 3 - 7 years of age, an annual incidence of 10-30 percent of ovarian and oviductal adenocarcinomas occur. There are 5 times as many ovarian tumors as oviductal. The primary tumors grow to a large size and implant onto the serosa of visceral organs, causing intestinal obstruction and ascites. Histologic appearance of the ovarian tumors is uniform, with formation of glandular type tissue; reactive smooth muscle proliferation, at sites of implantation, is notable. RIA measurements of steroid sex hormones have been made for plasma samples of hens according to their egg production, and for samples from tumor-bearing hens. Definite patterns of plasma hormone levels have been identified which indicate aberrancies in tumorous hens, particularly in progesterone. Pituitary hormone levels are presently being measured and further assays of steroid hormones are being made, in a prospective study made possible by identification of hens at greatest risk. Additional objectives of this study are to: culture ovarian tumor cells; examine plasma of tumor-bearing hens for presence of a tumor-associated antigen; and to try to detect presence of oncornaviruses in tumor tissues.